SECTION 3
Directions: Each passage in this group is followed by questions based on its content. After reading a passage, choose the best answer to each question. Answer all questions following a passage on the basis of what is stated or implied in the passage.
Scientists have long speculated as to the extent that inbreeding contributes
to the decline and eventual extinction of large assimilated populations, most
agreeing that in natural populations the impact of inbreeding depression on
Line population survival is insignificant in comparison to that of demographic and
(5) environmental variables. While there is ample evidence of fitness reduction due
to inbreeding depression in captivity, no field studies on natural populations
have been conducted to test the proposed effect on extinction.
However, Saccheri recently found in his study of a large metapopulation of
the Glanville .fritillary butterfly that extinction risk increased significantly
(10) with decreasing heterozygosity, an indication of inbreeding, even after
accounting for the effects of the relevant ecological factors. Rate of maturation,
larval survival, adult longevity and egg-hatching rate were found to be adversely
affected by inbreeding, and appear to be the fitness components underlying the
relationship between inbreeding and extinction. One wonders, nevertheless,
(15) how applicable these results would be to the increasing number of species with
small isolated populations due to habitat loss and fragmentation.
Which of the following best describes the organization of the passage？

A common viewpoint is presented, its insufficiency is pointed out and a solution is suggested but qualified.
B. A thesis is presented, and a scientific study is cited in support, then criticized.
C. A question is articulated, two possible solutions are offered, then one is decided upon.
D. A scientific study is explained, its results questioned, and a new thesis is formed.
E. A thesis is articulated, then a scientific study is explained which leads to a new thesis.